Purpose: To study whether residual metabolically active areas within esophageal tumors can be identified by areas of high FDG uptake on the pre-chemoradiotherapy (CRT) PET/CT scans. This will allow dose escalation to these areas at the highest risk for residual tumor in order to improve outcomes.

Methods: Twenty patients were included from a prospectively collected database. A rigid registration was used to align the post-CRT PET/CT with the pre-CRT PET/CT images. The primary tumor and the residual metabolically active areas were delineated using a region-growing algorithm with a threshold of standard uptake value (SUV) = 2.5 on the pre-CRT and post-CRT images, respectively. Seven areas of high FDG uptake pre-CRT were delineated using thresholds of SUV 2.5, 5.0, 34%, 40%, 50%, 60%, and 70% of the maximal SUV, respectively. Overlap fraction and centroid distance were computed to quantify the similarity and proximity between these areas and the residual areas.

Results: Six of the 20 patients had residual metabolically active areas within the primary tumor on the post-CRT PET/CT. Representative images were shown to illustrate four different relationships between the primary tumors and the residual areas. The average overlap fractions between areas of high FDG uptake pre-CRT and the residual areas were all less than 60%. The average centroid distances were all greater than 8.6 mm, and increased as the threshold increased. Areas of higher FDG uptake pre-CRT had lower overlap and larger distance to the residual areas post-CRT.

Conclusions: The results suggested that pre-CRT PET/CT can not reliably identify the residual metabolically active areas in esophageal cancer. Selective dose escalation to areas of high FDG uptake may not be benefit for many patients.

This work was supported in part by the National Cancer Institute Grant R21 CA131979.